Field of the Invention
The present invention relates to a feeding device of a belt drying installation for dump or sewage sludge material that has been dewatered to a pasty consistency and to a method for controlling such a feeding device.
Drying installations having a belt dryer as the core component (hereunder referred to as a belt drying installation) allow continuous drying methods based on the principle of convection to be carried out efficiently. As is shown in FIG. 1 by means of a typical belt drying installation 1 by the applicant, the material 60 to be dried herein continuously as a pile 62 that is as uniform as possible is fed by means of an infeeding conveyor unit 80, a metering unit 81, and by means of a feeding device 10 that is disposed in the transportation path T and is adapted to the material 60 onto an air-permeable conveyor belt 20. Feeding as a pile 62 has the effect of an enlargement of the specific surface area of the material 60 to be dried, this being a precondition for the intensive evaporation of water and optimal drying.
Following distribution onto the transportation belt 20, the pile 62 in a gentle and static manner runs through a tunnel-type drying zone 30, said pile 62 at the end of the latter being dropped as dried goods 63 onto an outfeeding conveyor unit 82. Both the mechanical wear on the installation 1 as well as the formation of dust accumulations are reduced and the risk of any explosion is thus eliminated by avoiding any friction of the pile 62.
The drying zone 30 is usually subdivided into individual drying chambers 31, 32, . . . The pile 62 in the individual chambers 31, 32, . . . of the drying zone 30 is perfused by hot air 41 which in most fields of application is guided in circulation by a ventilation system 40. The modular construction of a drying zone 30 from chambers 31, 32, . . . enables capacity to be readily expanded by inserting additional drying chambers 33, 34, . . . Drying is performed in the low-temperature range at approx. 80 to 140° C.
The air that is humidified in the belt dryer 1 is evacuated from the drying zone 30 by means of an exhaust air blower 42 and is guided through a series of heat exchangers 50: a first of the latter lowering the temperature of the drying air; the air being further cooled in a second condenser stage; the vapors being condensed on account thereof. The recirculated air is subsequently heated again in a third stage. This system enables the dryer exhaust air to be largely recycled and the energy requirement to be reduced by internal heat recovery.
Known belt drying installations usually operate at high availability in a safe temperature range. The former can be individually adapted to existing energy sources (steam, hot water, thermal oil, natural gas, heating oil, exhaust heat from the operation of CHP plants, gas engines, engine exhaust gas) such that available energy can be utilized in an optimal manner. To the extent that exhaust gases are to be employed as an energy source, reference is made pertaining to the environmentally friendly preparation of said exhaust gases to the entire cleansing method as disclosed by the applicant in DE 11 2011 100 511 A5.
Industrial or communal sludge material which is generated in open dump ponds or water treatment plants, etc., is often contaminated with the most varied of foreign matter such as, for example, metallic particles, rocks, hair, bristles, ear swabs, roots, pieces of timber, plastics parts, or the like.
To the extent that sludge material is to be used as goods to be dried, it is known for the former to be dewatered to a pasty consistency.
Furthermore, units for forming sausage-shaped moldings from pasty sludge material, which are configured as a feeding device of a belt drying installation and squeeze the previously dewatered sludge material through a perforated die, for example with the aid of a ram, are known from JP 2012-179591 A for example. Sausage-shaped moldings which are infed to a belt dryer for the purpose of effectively drying the sausage-shaped moldings are created herein.
However, when sludge material that is dewatered to a pasty consistency is conveyed through a perforated die there is the risk of individual passage bores being clogged by virtue of the foreign matter that is usually included in the sludge material. This is also the case when the sludge material has previously been squeezed through a screen and has been largely relieved of coarse foreign matter, the dimensions of the latter being larger than the diameter of the passage bores in the perforated die. In particular, hairs or other fibrous impurities such as bristles, plastics threads, or wood fibers, etc., are often by way of one end thereof pushed through another passage bore of the perforated die than by way of the other end thereof. This leads to a constriction of the cross section and subsequently to clogging of the passage bores, with the consequence that perforated dies of this type have to be cleaned frequently.
In order for clogging of this type by virtue of fibrous impurities to be avoided or eliminated, respectively, a perforated die that is embodied in two parts is known from DE 40 13 760 C2, for example, wherein an upper part of the perforated die is configured as a shearing plate that bears on the main face of a main part and is disposed so as to be displaceable in a reciprocating manner on the main part of the die, such that fibrous impurities that are included in the sludge material and adhere to and in the passage bores are sheared.
The passage holes mentioned extend through both the main part as well as the shearing plate. However, to the extent that a perforated die that is configured in such a manner in two parts is impacted by coarse foreign matter such as in particular crown caps, small rocks, or equivalent non-shearable foreign matter, the process for producing the sausage-shaped moldings has to be interrupted, as before. Therefore, the known installation is also not capable of continuous production while the non-shearable foreign matter is being removed. A substantially continuous operation is thus not guaranteed.
Furthermore, a feeding device of a belt drying installation for dump or sewage sludge material that has been dewatered to a pasty consistency in which in the transportation path of the sludge material at least                one first roller having transverse grooves that are set back in relation to the external diameter of said first roller, and        at least one guiding means relative to the external diameter of the first roller, are disposed such that when the first roller is rotated the sludge material is drawn into the transverse grooves and molded into elongate extruded pressings, are known from JP 2003-227684 A or from CN 103 623 745 A, for example.        
By contrast to perforated dies which typically tend to clog, the employment of at least one roller having transverse grooves formed therein has the advantage that impurities when placed transversely across two or more transverse grooves are comminuted by shearing and moreover are entrained and are enclosed in the extruded pressing, as is other foreign matter.
A combined device for drying sludge and other pasty materials, composed of a grooved-roller dryer and a downstream belt dryer or drum dryer or another type of hot-air dryer is known from DE 20 2010 007 475 U1 for example, wherein the grooved-roller dryer is installed in an insulated housing, and is equipped with one or a plurality of impact jet drying elements (tubes having nozzles) for additionally drying by way of hot air the pasty mass that is dried from three sides by contact drying in the grooves.
Reference is finally to be made to WO 2006/075920 A1, CN 202 322 581 U, and DE 47 162 A1.